Activated neutrophils inhibit Na(+)-K(+)-ATPase in canine renal basolateral membrane

To examine the effects of activated neutrophils (PMNs) on Na(+)-K(+)-ATPase, phorbol 12-myristate 13-acetate (PMA)-stimulated PMNs were incubated with canine renal cortical basolateral membrane (BLM), and BLM ouabain-sensitive Na(+)-K(+)-ATPase activity was subsequently quantified. Na(+)-K(+)-ATPase activity decreased to 40.0 +/- 8.7% (SE) of control in the presence of activated PMNs, from 0.89 +/- 0.12 to 0.34 +/- 0.05 mumol Pi.mg protein-1.min-1. This inhibition coincided with a decrease in the apparent Michaelis constant (Km) for ATP from 0.18 +/- 0.02 to 0.05 +/- 0.01 mM. Inclusion of catalase (CAT) and superoxide dismutase (SOD) in the BLM/PMN/PMA incubation mixture resulted in partial preservation of enzyme activity, with an increase to 57.0 +/- 4.6% of control with CAT alone and to 70.0 +/- 5.3% with both CAT and SOD. SOD alone had no protective effect. Neither the myeloperoxidase inhibitor azide nor the hypochlorous acid scavenger L-methionine preserved enzyme activity. Hydroxyl radical scavengers and iron chelators were also ineffective in attenuating Na(+)-K(+)-ATPase inhibition by activated PMNs. These results indicate that activated PMNs mediate a decrease in BLM Na(+)-K(+)-ATPase activity characterized by a reduction in maximum velocity and Km for ATP that appears to be mediated in part by reactive oxygen metabolites.